Molecular mechanism of estrogen action to inhibit obesity

雌激素不仅对雌性生殖器官，而且对非生殖器官，包括脂肪组织，都有多种作用。雌激素抑制啮齿动物卵巢切除引起的肥胖。我们研究了这种雌激素依赖性抑制肥胖的机制。雌激素显着降低脂肪积累和脂蛋白脂酶（LPL）的mRNA的量，以及在基因操作的3 T3-L1脂肪细胞稳定表达雌激素受体（ER）的甘油三酯的积累。然后研究雌激素对小鼠LPL基因的转录调控。将pLPL（1980）-CAT构建体与ER表达载体一起沿着导入分化的3 T3-L1细胞中。测定CAT活性。ER，主要是配体依赖性，抑制基础LPL启动子活性的7倍。我们通过使用一组pLPL-CAT报告基因的5 ′-缺失突变体来搜索LPL启动子中的雌激素应答抑制元件。虽然没有经典的雌激素反应元件，但已证明位于（-1856/-1850）的AP-1样TGGAATTC序列负责雌激素对LPL基因转录的抑制。用TGAATTC序列探测的电泳迁移率变动分析表明形成了特异性DNA-核蛋白复合物。有趣的是，该复合物不受添加针对ER、c-Jun、c-Fos、JunB或JunD的任何抗体的影响。这些结果可能表明，存在一个独特的信号通路，利用一个独特的雌激素反应元件以外的经典ERE和结合蛋白，可能调节LPL基因的转录。

Estrogen exerts a variety of effects not only on female reproductive organs but also on nonreproductive organs, including adipose tissue. Estrogen inhibits obesity trggered by ovariectomy in rodents. We studied the mechanism underlying this estrogen-dependent inhibition of obesity. Estrogen markedly decreased the amounts of fat accumulation and lipoprotein lipase (LPL) mRNA as well as triglyceride accumulation in genetically manipulated 3T3-L1 adipocytes stably expressing the estrogen receptor (ER). Transcriptional regulation of the murine LPL gene by estrogen was then studied. A pLPL (1980)-CAT construct, along with an ER expression vector, was introduced into differentated 3T3-L1 cells. and CAT activities were determined. ER, mostly ligand-dependently, inhibited the basal LPL promoter activity by 7-fold. We searched the LPL promoter for an estrogen-responsive suppressive element by employing a set of 5'-deletion mutants of the pLPL-CAT reporter. Although there was no classical estrogen response element, it was demonstrated that an AP-1-like TGGAATTC sequence located at (-1856/-1850) was responsible for the suppression of the LPL gene transcription by estrogen. An electrophoretic mobility shift assay probed with the TGAATTC sequence demonstrated formation of a specific DNA-nuclear protein complex. Interestingly, this complex was not affected by the addition of any antibodies against ER, c-Jun, c-Fos, JunB, or JunD. These results may indicate the existence of a unique signaling pathway utilizing a unique estrogen response element other than classical ERE and binding proteins which possibly regulate transcription of the LPL gene.